The present invention is generally related to automatic transmissions. More particularly, the present invention pertains to a hydraulic pressure control device which produces various gear stages of an automatic transmission.
A hydraulic pressure control device for an automatic transmission is designed to control the hydraulic pressure fed to a plurality of friction elements. This involves the use of a linear solenoid valve which adjusts the hydraulic pressure outputted from an oil pump, a control valve receiving the outputted hydraulic pressure for generating the control pressure which is to be applied to each of the friction elements, and a shift valve whose position is adapted to be switched to make it possible to apply the control pressure to one or more of the desired friction elements.
In some gear train arrangements, differences may exist with respect to the control pressure required to effect engagement. With the arrangement mentioned above, the switching of the shift valve causes the control pressure outputted from the single control valve to be applied to the required plural friction elements. This means that even if the friction elements to be applied with the control pressure change, the magnitude of the control pressure remains unchanged. That is, although various ones of the friction elements may require different control pressures (i.e., a different magnitude of control pressure) for effecting engagement of the friction elements, the magnitude of the control pressure outputted from the single control valve is the same. Thus, with a construction such as that described above, by controlling the linear solenoid valve and the control valve, the magnitude of the control pressure outputted from the single control valve corresponds to the greatest magnitude of hydraulic pressure required for engaging the friction elements.
However, in this type of arrangement, although a control pressure having adequate magnitude may be applied to one or more of the friction elements, an excessively high control pressure is applied to various other ones of the friction elements. Thus, the balance in the hydraulic pressure to be applied to the friction elements becomes worse, which lowers the hydraulic control performance, whereby undesirable shift shock may occur and/or an adverse affect may occur in the lower area of engine idling.
Thus, a need exists for improved shift control performance in a hydraulic control device for an automatic transmission.
It would thus be desirable to improve the shift control performance in an automatic transmission hydraulic control device in which control pressure is applied from a single control valve to a plurality of friction elements.
According to one aspect of the invention, a hydraulic pressure control device for an automatic transmission, in which control pressure is applied to and drained from each of a plurality of friction elements to produce various gear stages, includes an adjusting mechanism for adjusting hydraulic pressure from an oil pump to produce an outputted hydraulic pressure, and a control valve receiving the outputted hydraulic pressure from the adjusting mechanism for generating the control pressure to be applied to at least some of the friction elements whose magnitude depends on a magnitude of the outputted hydraulic pressure. The control valve includes a control port from which the control pressure is outputted, a first feed back port to which the outputted control pressure is adapted to be fed back, and a second feed back port to which the outputted control pressure is adapted to be fed back. A shift valve receives the control pressure from the control valve and is selectively positionable in a first position for applying hydraulic pressure to the first friction element and a second position for applying hydraulic pressure to the second friction element. The shift valve is operated in such a manner that fluid communication between the control port and each of the first and the second feedback ports is controlled to lower the control pressure from the control valve when the shift valve is in the second position relative to the control pressure from the control valve when the shift valve is in the first position. A switching device is provided for switching the shift valve between the first position and the second position.
In accordance with the present invention, the first feedback port and the second feedback port are provided in the control valve, and fluid communication between the control port and the first and second feedback ports is communicated or interrupted by the shift valve. Thus, the control pressure when outputted from the control valve for being applied to the first friction element differs from the control pressure outputted from the control valve for being applied to the second friction element.
Thus, even if the friction elements are applied with control pressure from a single control valve, the magnitude of the control pressure applied to each friction element can be adequate and generally consistent with the required pressure, thus improving the hydraulic pressure control performance upon gear stage change. This thus improves the shift control performance by, for example, reducing the shift shock and/or lessening any adverse effect of engine idling when the gear stage is changed.
In accordance with another aspect of the invention, a hydraulic pressure control device for an automatic transmission in which control pressure is applied to and drained from a plurality of friction elements to produce various gear stages includes a linear solenoid valve connected to a pump to adjust hydraulic pressure from the pump and produce an outputted hydraulic pressure, and a control valve fluidly connected to the linear solenoid valve to receive the outputted hydraulic pressure from the linear solenoid valve and generate the control pressure to be applied to at least a first one of the friction elements and a second one of the friction elements. The control valve has a control port from which the control pressure is outputted, a first feed back port receiving control pressure and a second feed back port receiving control pressure. A shift valve is fluidly connected to the control valve to receive the control pressure from the control valve, with the shift valve including a movable valve main body, a first shift port connected to the first friction element, a second shift port connected to the second friction element, and a control pressure adjusting port connected to the second feed back port of the control valve. An ON-OFF solenoid valve is connected to the shift valve to move the valve main body between a first position in which the hydraulic pressure is applied to the first friction element and is prevented from being applied to the second friction element and the control pressure is supplied to the first feed back port of the control valve while being prevented from being supplied to the second fee back port of the control valve, and a second position in which the hydraulic pressure is applied to the second friction element and is prevented from being applied to the first friction element and the control pressure is supplied to the second feed back control port of the control valve by way of the control pressure adjusting port and to the first feed back port of the control valve.
According to another aspect of the invention, a method of controlling hydraulic pressure in an automatic transmission in which control pressure is applied to and drained from each of a plurality of friction elements to produce various gear stages involves producing one gear stage by supplying control pressure from a control valve to a first one of the friction elements by way of a shift valve while preventing control pressure from being supplied to a second one of the friction elements by way of the shift valve, and producing a different gear stage by supplying control pressure from the control valve to the second friction element by way of the shift valve while preventing control pressure from being supplied to the first friction element by way of the shift valve. The control pressure supplied to the second friction element during the different gear stage is less than the control pressure supplied to the first friction element during the one gear stage.